(a) Field of the Invention
The present invention relates to a RF relay of a full-duplex, and a method of removing interference of an electromagnetic wave level thereof.
(b) Description of the Related Art
In a cellular system, in order to improve spectral efficiency and extend coverage, a repeater is used between a base station and a terminal. An optical repeater and a wireless repeater or radio frequency (RF) relay are used as the repeater.
The optical repeater receives a signal through an optical cable and retransmits the signal, and thus interference does not occur between a transmitter and a receiver. However, much cost is required to install an optical cable, and particularly, when a small number of users exist in a wide area, it is inefficient to construct an optical cable infrastructure.
Recently, research on a RF relay of which installation cost is less than that of an optical repeater and that can freely select an installation area has been actively performed. The RF relay receives a radio frequency (RF) signal with a receiving antenna and retransmits the RF signal with a transmitting antenna. A duplexing method of such a RF relay is classified as a half-duplex method and a full-duplex method. Because the half-duplex RF relay transmits and receives a RF signal using two orthogonal channels in a time domain or a frequency domain, interference of a transmitting signal does not exist in a receiver. On the other hand, because the full-duplex RF relay simultaneously transmits and receives a RF signal, the full-duplex RF relay has very high spectral efficiency, but it is difficult to physically implement the full-duplex RF relay due to interference of a transmitting signal.
Various methods of removing an interference signal in order to implement a full-duplex RF relay have been suggested. Representatively, a method of removing an interference signal by processing a radio frequency signal that is received in the receiving antenna or a method of removing an interference signal through digital signal processing after converting an intermediate frequency signal to a digital signal is used.
According to such interference removing technology, after an interference signal that is generated in the transmitting antenna is received in the receiving antenna, the RF relay processes the interference signal. That is, after an interference signal is received, the interference signal is removed through post-processing and thus there is a limitation in improving performance of the RF relay. Further, because power intensity of an interference signal is much greater than that of a received signal that is received from a base station, a problem of signal distortion due to non-linearity of a low noise amplifier in a receiver of a RF relay and signal distortion due to resolution insufficiency of an analog to digital converter (ADC) when converting to a digital signal cannot be solved. Further, because much time is required for signal processing for removing an interference signal, there is a problem that a delay time is lengthened in the RF relay.
Further, a method of removing interference signal in an electromagnetic wave (EM) level by greatly increasing the distance between a transmitting antenna and a receiving antenna has been proposed, but when installing such a RF relay, the RF relay can only be used in a partial environment due to spatial restrictions. Therefore, a method of removing interference of an EM level is required so that an interference signal that is generated in a transmitting antenna is not received in the receiving antenna without greatly increasing the distance between the transmitting antenna and a receiving antenna of a full-duplex RF relay.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.